(1) Field of the Invention
The present invention relates to a switching control technique in an optical switching device, and more particularly to a controlling apparatus and a controlling method of an optical switching device utilizing reflection type tilt-mirrors based on a micromachining (MEMS: Micro Electric Mechanical system) technique.
(2) Description of the Related Art
Recently, an increase in traffic in the Internet and the like has resulted in an increased demand for optical networks. Under these circumstances, attention has been directed to the introduction of an optical switching device for directly switching large-capacity and high-speed data in the form of optical signals. Conventional techniques for realizing such an optical switching device having the nature of large capacity and high speed have mainly included methods for mechanically switching optical fibers, for combining waveguides with one another or the like. However, in such conventional techniques, a multistage constitution is required to be adopted, thereby resulting in an extremely large optical loss within the optical switching device and resulting in limitations in coping with the increase of the number of channels, so that it has been difficult to realize an optical switching device capable of coping with several tens or more channels.
Under the above circumstances, attention has been directed to an optical switch utilizing tilt-mirrors (hereinafter called “MEMS mirrors”) fabricated by applying a micromachining (MEMS) technique, since such an optical switch is superior to other switches in terms of downsized, wavelength independency and polarization independency, for example. Particularly, for example, as shown in FIG. 45, an optical switching device of three-dimensional type constituted by combining two collimator arrays 1A, 1B each having a plurality of collimators two-dimensionally arranged and two MEMS mirror arrays 2A, 2B each having a plurality of MEMS mirrors two-dimensionally arranged, is expected since reduction of an optical loss, increase of the capacity, and realization of multiple channels are possible.
In the aforementioned three-dimensional type optical switching device utilizing the MEMS mirror arrays 2A, 2B, however, due to angle deviations between MEMS mirrors, it is likely that deviations occur in inputs of optical signals to output fibers connected to output side collimators, thereby causing a factor which increases the optical loss within the optical switching device.
FIG. 46 exemplarily shows the above content, in which FIG. 46A is a plan view showing an example of an optical path from an input point to an output point of an optical signal in the optical switching device, and FIG. 46B is a plan view exemplifying respective states where optical signals are input to output fibers, respectively. Note, in FIG. 46, input side and output side collimators are omitted, so as to comprehensively show the states of optical paths in the optical switching device.
In FIG. 46, a light reflected by an output side MEMS mirror is required to be input perpendicularly to a core portion of an output fiber, as indicated by “OK” in FIG. 46B, and such a light should not be deviated from the core as indicated by “NG1” and “NG3” nor obliquely input to the core as indicated by “NG2” in FIG. 46B.
Such defective coupling of an optical signal to an output fiber is caused by a slight angle deviation, even if an input port and an output port of the optical signal have been determined, and angles to be controlled for respective input side and output side MEMS mirrors are known numeric values. Specifically, an angle deviation of the order of 0.050° in MEMS mirror causes an optical loss of a few dB. Concerning angle deviations of MEMS mirrors, it is difficult to judge which one of paired MEMS mirrors is deviated and how much the deviation is, because it is impossible to individually monitor the optical signal power corresponding to the angle of each mirror.
To correct the aforementioned angle deviations of MEMS mirrors, it is conceivable a method to detect light position information of an optical signal propagated from an output side MEMS mirror to an associated collimator, such as by a CCD image sensor. However, it is not easy for this method to detect differences between the “OK” and “NG2”, and between the “NG1” and “NG3” in FIG. 46B. Namely, such a method has a defect in that it is difficult to detect incident angle information of light. Particularly, in the state of “NG2”, it is difficult to judge whether or not the light is being correctly output.
As another method to correct angle deviations of MEMS mirrors, it is further conceivable a method to monitor, for example, the power of optical signal coupled to an output fiber, so as to feedback control the angle of each MEMS mirror based on the monitored result. In this method, however, it is impossible to adopt such a system to feedback control the angles of MEMS mirrors so that the monitored optical powers are brought to previously set initial values, because a target value of optical power of each channel can not be determined to be constant due to variations and the like in optical powers of multiple channels to be input to the optical switching device. Further, since it is also difficult to confirm whether or not the optical power presently being monitored is a maximum value, it is therefore difficult to realize the aforementioned feedback control.